#include <iostream>
#include <vector>
#include <list>
#include <iterator>
#include <algorithm>
#include <set>

using namespace std;

void test0(){
    vector<int> vec;
    vec.push_back(2);

    auto it2 = vec.end();
    bool flag = true;
    for (auto it = vec.begin(); it != it2; ++it) {
        cout << *it << endl;
        if(flag){
            vec.push_back(1);
            flag = false;
//            it = vec.begin();
        }
    }

}

/* 引用折叠 */
template<class T>
void test9(T&& a){
    a = 2;
}
int main() {
    int x = 1;
    int&& a = 3;
    test9(a);
    cout << a << endl;
//    test0();
    return 0;
}
